1. Field
The disclosed concept relates generally to electrical switching apparatus and, more particularly, to electrical switching apparatus, such as circuit breakers. The disclosed concept also relates to closing assemblies and to reversal prevention mechanisms for electrical switching apparatus.
2. Background Information
Electrical switching apparatus, such as circuit breakers, provide protection for electrical systems from electrical fault conditions such as, for example, current overloads, short circuits, abnormal voltage and other fault conditions. Typically, circuit breakers include an operating mechanism, which opens electrical contact assemblies to interrupt the flow of current through the conductors of an electrical system in response to such fault conditions as detected, for example, by a trip unit. The electrical contact assemblies include stationary electrical contacts and corresponding movable electrical contacts that are typically mounted on moving (e.g., pivotable) arms.
Among other components, the operating mechanisms of some power air circuit breakers, for example, typically include a trip actuator assembly, a closing assembly and an opening assembly. The trip actuator assembly responds to the trip unit and actuates the operating mechanism. The closing assembly and the opening assembly may have some common elements, which are structured to move the movable electrical contacts between a first, open position, wherein the movable and stationary electrical contacts are separated, and a second, closed position, wherein the movable and stationary electrical contacts are electrically connected. Elements of both the closing assembly and the opening assembly move (e.g., pivot) in order to effectuate the closing and opening of the electrical contacts. A charging assembly, which includes a stored energy mechanism, is often employed to facilitate operation of the closing assembly.
It can be difficult for some circuit breakers to close on a relatively high current fault, commonly referred to as a Hi-IC. In order to clear the fault, it is desirable that the electromagnetic forces caused by the Hi-IC not be permitted to blow the moving arms back, towards their opening position, once electrical current begins to flow. Such a condition is commonly referred to as, “blow back.” More specifically, at some level of fault current, the circuit breaker will not close completely (e.g., it stalls), and at even higher currents, the closing action will be reversed, blowing the arms and mechanism backwards. Separate devices exist for detecting a stalled condition, and to interact with the circuit breaker trip unit to fire the trip actuator and open the circuit breaker. The further the mechanism is from the fully closed position, the more difficult it is to trip the breaker for a given interruption current-induced electromagnetic force, because of poor mechanical advantage. Accordingly, preventing the moving arms and mechanism from blowing open facilitates the tripping process.
In stored energy circuit breakers where the stored energy mechanism (e.g., closing spring(s)) indirectly drive the mechanism through a cam shaft, a relatively complicated mechanical clutch on the cam shaft is used to prevent the mechanism from undesirably moving backwards. In other designs, such as for example where the stored energy mechanism (e.g., closing spring(s)) directly drives the mechanism, such a cam shaft clutch is ineffective.
There is, therefore, room for improvement in electrical switching apparatus, such as circuit breakers, and in closing assemblies and reversal prevention mechanisms therefor.